docs: def save_settings(self, filename):
          '''Save settings to a JSON file
  
          Arge:
              filename (string): name of the file to save to
          '''
  
          data = dict()
          data['valueRanges'] = self._value_ranges
          data['best_values'] = [str(value) for value in self._best_values]
          data['minimize'] = self._minimize
          data['num_employers'] = self._num_employers
          data['best_score'] = str(self._best_score)
          data['limit'] = self._limit
          data['best_error'] = self._best_error
          with open(filename, 'w') as outfile:
              json.dump(data, outfile, indent=4, sort_keys=True)